Optical matrix switches are commonly used in communications systems for transmitting voice, video and data signals. Generally, optical matrix switches include multiple input and output ports, and have the ability to connect, for purposes of signal transfer, any input port to any output port. Preferably, for N×M switching applications, optical matrix switches also enable multiple connections at one time. At each port, optical signals are transmitted and/or received via an end of an optical waveguide. The waveguide ends of the input and output ports are optically connected across a switch core. In this regard, for example, the input and output waveguide ends can be physically located on opposite sides of a switch core for direct or folded optical pathway communication therebetween, in side-by-side matrices on the same physical side of a switch interface facing a mirror, or they can be interspersed in a single matrix arrangement facing a mirror.
Establishing a connection between an input port and a selected output port, involves configuring an optical pathway across the switch core between the input ports and the output ports. One known way to configure the optical path is by moving or bending optical fibers using, for example, piezoelectric actuators. The actuators operate to displace the fiber ends so that signals from the fibers are targeted at one another so as to form the desired optical connection across the switch core. The amount of movement is controlled based on the electrical signal applied to the actuators. Two-dimensional targeting control can be affected by appropriate arrangement of actuators.
Another way of configuring the optical path between an input port and an output port involves the use of one or more moveable mirrors interposed between the input and output ports. In this case, the waveguide ends remain stationary and the mirrors are used to deflect a light beam propagating through the switch core from the input port to effect the desired switching. Microelectromechanical (MEMS) devices, known in the art, have mirrors disposed thereon that provide for two-dimensional targeting to optically connect any input port to any output port. For example, U.S. Pat. No. 5,914,801, entitled “Microelectromechanical Devices Including Rotating Plates And Related Methods”, which issued to Dhuler et al. on Jun. 22, 1999; U.S. Pat. No. 6,087,747, entitled “Microelectromechanical Beam For Allowing A Plate To Rotate In Relation To A Frame In A Microelectromechanical Device”, which issued to Dhuler et al. on Jul. 11, 2000; and U.S. Pat. No. 6,134,042, entitled “Reflective MEMS Actuator With A Laser”, which issued to Dhuler et al. on Oct. 17, 2000, disclose microelectromechanical systems (MEMS) having mirrors disposed thereon that can be controllably moved in two dimensions to effect optical switching.
U.S. Pat. No. 6,097,858, entitled “Sensing Configuration For Fiber Optic Switch Control System”, and U.S. Pat. No. 6,097,860, entitled “Compact Optical Matrix Switch With Fixed Location Fibers”, both of which issued to Laor on Aug. 1, 2000, disclose switch control systems for controlling the position of two-dimensionally movable mirrors in an optical switch. The mirrors can allow for two-dimensional targeting to optically connect any of the input fibers to any of the output fibers.
An important consideration in optical switch design is minimizing physical size for a given number of input and output ports that are serviced, i.e. increasing the packing density of ports and beam directing units. It has been recognized that greater packing density can be achieved, particularly in the case of a movable mirror-based beam-directing unit, by folding the optical path between the ports and the movable mirror and/or between the movable mirror and the switch interface. Such a compact optical matrix switch is disclosed in U.S. Pat. No. 6,097,860. In addition, further compactness advantages are achieved therein by positioning control signal sources outside of the fiber array and, preferably, at positions within the folded optical path selected to reduce the required size of the optics path.
Another example of a compact optical switch is disclosed by Laor in WO 99/66354, entitled “Planar Array Optical Switch and Method”. The optical switch disclosed therein includes two arrays of reflectors and a plurality of input and output fibers associated with a respective reflector on one of the arrays. The optical signal is directed along a “Z-shape” optical path from the input fibers via the first array of reflector and the second array of reflector to the output fibers.
However, the design of these prior art optical switches is such that the optical components are arranged along the optical path in a “Z-shape” pattern. A “Z-shape” arrangement of optical components is not spatially efficient. Furthermore, the number of input and output ports would determine the physical size of the optical switch. A plurality of input/output locations is provided so that the input and output beams can enter/exit the switching core. These input/output locations are commonly provided in the form of rectangular or other arrays.
Referring to FIG. 1, a schematic presentation of a prior art optical switch 100 having a Z-shaped arrangement of optical components is shown. A light beam is launched into an input fiber of input fiber bundle 116 and switched to a selected output fiber of output fiber bundle 118 along a Z-shaped optical path through switch 100, wherein micro-mirrors 110 on MEMS chips 112 are used to fold the design. Such a folded optical pathway configuration allows for a more compact switch design using a movable mirror based beam directing unit. However, the general approach in prior art optical switches is to individually collimate the beam from each input fiber and to direct this beam to its dedicated mirror. This mirror then deflects the beam to any one of the plurality of output mirrors which then redirects the beam, i.e. compensates for the angle, to its dedicated output fiber. As is seen from FIG. 1, this design requires the use of a lens 114 for each individual input fiber of input fiber bundle 116 and each individual output fiber of output fiber bundle 118.
The Z-shape approach for switching an optical signal requires particular consideration with respect to the physical spacing between the optical elements since the beam of light should not be obstructed by any of the optical elements along the optical path through the switch. It is apparent that this is not an efficient design since physical size requirements are not optimized in such an “off-axis” design.
The present invention provides an optical switch having an “on-axis” design, and hence it can provide a more compact optical switch than the prior art. In addition, arranging an angle-to-offset (ATO) element between the deflection elements provides for a re-imaging, and hence a small and low loss optical switch can be provided in accordance with the invention.
Accordingly, it is an object of the invention to provide a compact optical switch.
It is a further object to provide a switch with improved spatial efficiency in order to minimize a physical size of the optical switch for a given number of input/output ports.
Another object of this invention is to provide a compact optical cross-connect arrangement.
Another object of this invention is to provide a compact optical switch based on deflection means in transmission.